We performed experiments designed to establish a stable lymphatic endothelial cell (LEC) line with an extended life span that can be used as a model to study lymphatic endothelial cell biology and pathophysiology. A transformed line of lymphatic endothelial cells was obtained by infecting monolayers of LEC with SV40 DNA using the calcium phosphate method of transfection. The cell line (SLET-1) obtained in the present study showed a marked increase in growth potential without the need of mitogenic factors (growth factors) to stimulate and sustain a rapid growth rate. This growth rate was also maintained when cells were plated on uncoated culture dishes in the absence of serum. The endothelial features retained by the SLET-1 cell line include the ability to form confluent monolayers and the production of von Willebrands Factor and plasminogen activators. In addition, at confluence the SLET-1 cells continued their rapid growth and became multilayered. The ability of the SLET-1 cell line to undergo lymphangiogenesis when treated with endothelial cell growth factor makes it a useful in vitro model for studies of lymphatic endothelial cell function and differentiation. - endothelial cells; lymphatics; histochemistry; tissue culture; electron microscopy.